There exists a number of processes in industry where it is desirable to treat a specimen or workpiece with a particular gas at an elevated temperature and pressure. Where the gas is corrosive or reactive with the pressure vessel and/or the electrical heating elements, a substantial problem exists. Double chambered pressure vessel/furnaces in which a container is mounted within a pressure vessel and divides the vessel into two chambers, i.e., a furnace chamber containing the heating elements and an isolated process chamber containing the specimen are known. Further, in the past, the container defining the inner chamber has been constructed with a lesser thickness than the pressure vessel. Hence, the differential pressure was controlled to prevent the change in shape of the inner container.
It is an advantage according to this invention that the furnace is divided into a furnace chamber and process chamber by an inner container attached to the front cover of the pressure vessel. Accessibility to the process chamber is very good due to the separate small front closure which can be easily removed. In other words, one end-wall of the process chamber is the end-wall of the pressure vessel and, in particular, a removable portion of that end-wall.
It is an advantage according to this invention to provide a pressure vessel/furnace suitable for oxidation of silicon wafers in the manufacture of integrated circuit chips. The workpiece may be heated to a temperature of 1000.degree. C. in an oxygen atmosphere at 15,000 psi. It is a further advantage to provide a wafer oxidation furnace with superior cleanliness and extremely good temperature uniformity in the process chamber. A uniformity of about .+-.1.degree. Centigrade is desired. The furnace has associated with it sources of pressurizing, blanketing and processing gases and means for drawing a vacuum on the process chamber. The furnace inner container keeps the process chamber clean, which is very critical for silicon oxidation work. Possible contaminates from the furnace installation will be kept in the furnace chamber gas which is usually argon, helium or nitrogen. The process gas is isolated from the vessel by the furnace inner container, therefore it can be hydrogen or oxygen. Embrittlement and oxidation are kept to a minimum and affect only inexpensive parts such as the inner container and the small cover. The furnace inner container is attached to the cover of the pressure vessel/furnace and can be replaced easily.
Briefly according to this invention, there is provided a double chambered high pressure furnace for treating specimens and workpieces with process gases at elevated temperatures and pressures. The high pressure furnace comprises a cylindrical pressure vessel with a rear closure for sealing one end of the vessel and an apertured front closure for partially sealing the other end of the vessel. An electrical heating element is supported within the interior of the cylindrical pressure vessel near the inner wall thereof from the rear closure. A relatively thin-walled inner container is supported from the front closure and opens only to the aperture in the front closure. The inner container interior defines a process chamber and the inner container exterior along with the pressure vessel and end closures defines a furnace chamber. The process chamber is completed by a small closure for plugging the aperture in the front closure of the vessel. The front closure, small closure and rear closure devices are secured, for example, by a reaction frame. Passageways are provided for introducing blanket gases to the furnace chamber and process gases to the process chamber under high pressures. Sensors detect the differential pressure across the inner container and control valves which maintain the pressure difference across the inner container small so the inner container maintains its original shape.
Preferably, according to this invention, the inner container has a passageway therein opening into the process chamber at the end opposite the small closure. This passageway is in communication with a passageway in the front closure thereby permitting the purging of the process chamber by the introduction of purge gases at the back thereof. It is an advantage of this embodiment that the process gases are heated prior to reaching the process chamber. Thus, they do not tend to quench the workpiece.